Cable modems that are being deployed today allow high-speed Internet access in the home over a cable network, often referred to as a hybrid fiber coax (HFC) network. Cable modems (CM) are units, often referred to as customer premises equipment (CPE), that are connected to a personal computer (PC) or other computing device, for example. A cable modem is adapted to communicate with a cable modem termination system (CMTS) that may include a cable network provider's headend. A cable modem is a modulator/demodulator that receives Internet traffic or information, data, TV signals, and telephony from a server through the CMTS and puts it into a format recognizable by a user's PC, allowing a user to browse the Internet, and send/receive e-mail just as they would with a conventional modem on a PC. Using a cable modem over a cable network provides a much faster connection, being at least 10 times faster than a 56K modem, for example.
A cable modem performs modulation and demodulation and the operations necessary to interface with a PC or a local area network (LAN). A cable modem typically comprises a transmitter for upstream modulation of a data signal, usually in short bursts. The upstream direction refers to sending a data signal from the user at the cable modem towards the headend that serves as an upstream demodulator. The upstream signal may comprise a TV channel, program selection or Internet data request information, for example, and may be a Quadrature Phase Shift Keying (QPSK)/16-Quadrature Amplitude Modulation (QAM) signal at 3 Mbit/s, for example. The cable modem also comprises a receiver for downstream demodulation of signals received from a transmitter in the headend that serves as a downstream modulator. The downstream direction refers to sending a data signal from the headend to the cable modem. The downstream modulation/demodulation may be 64-QAM/256 QAM at 27-56 Mbit/s, for example. Both the cable modem and headend include MACs that control the media access control (MAC) sublayer of the communication network. The communications between a cable modem and a CMTS typically are in accordance with an Internet protocol (IP)/Ethernet standard and the Data Over Cable Service Interface Specification (DOCSIS) standard.
In the U.S., signals are transmitted over a 100-860 Mhz range in increments of 6 Mhz to each cable modem user, with the CMTS servicing a hundred or so cable modem users, illustrated in the prior art drawing of FIG. 1. Each carrier 22 occupies 6 Mhz (8 Mhz in Europe). The CMTS 10 comprises a plurality of transmitters 12, each having a MAC 14 associated therewith. Each transmitter 12 is adapted to transmit data over the cable network at a particular frequency having a bandwidth of 6 MHz to cable modems 16 (typically many more than one) that have been assigned that frequency. Cable modem 16 comprises a receiver 18 and has a MAC 20 associated therewith for receiving the data.
A problem with the network architecture shown in FIG. 1 is that the CMs serviced by the network have to be distributed between multiple 6 MHz carriers in order to provide the required throughput to each CM. This separation imposes constraints on the network management and causes inefficient utilization of the bandwidth.
What is needed in the art is a more efficient way of utilizing the bandwidth, enabling the servicing of more cable modems 16 and/or enabling more throughput for each cable modem.